As early as the second scene, we see that Cassius is bitter over Caesar's newly won power. He describes an incident when he helped rescue Caesar from drowning, and remarks sardonically, "and now this man is become a god, and Cassius a wretched creature." In the same scene, he is already plotting against Caesar, and tries to persuade Brutus to join the cause. As he attempts to gain support for his plan, he constantly refers to loyalty to Caesar as slavery that is not to be tolerated. He also sees Caesar's rise to power as a sign that Romans have become weak and corrupted:

And why should Caesar be a tyrant then?Poor man! I know he would not be a wolf But that he sees the Romans are but sheep. He were no lion, were not Romans hinds. Those that with haste will make a mighty fire Begin it with weak straws. What trash is Rome,What rubbish and what offal, when it serves For the base matter to illuminate So vile a thing as Caesar?

It is Cassius that persuades Brutus to join, and he even proposes that the conspirators assassinate Marc Antony as well, a suggestion that Brutus (perhaps unwisely) rejects. Later Cassius objects, but ultimately defers to, Brutus's decision to allow Antony to speak over Caesar's body. Ultimately, Cassius is convinced that Caesar's actions are bad for Rome. But he also, very much unlike Brutus, personally detests Caesar.